This application is the U.S. National Phase of PCT Application Number PCT/GB03/00373, filed on 29 Jan. 2003, which claims priority to Great Britain Application Number 0202142.6, filed 30 Jan. 2002.
This invention relates to a watercraft which may be used for sailing using wind power, but which can maintain a level trim when mechanically propelled at high speeds.
1. Field of Invention
Sailing craft can be provided with a displacement mono-hull with a transverse cross-section which tapers downwardly on each side to its keel line, and which increases in cross-section from the bow to a fullest transverse section, and decreases in cross section from the fullest transverse section to the after end. Such a mono-hull shape is suitable for sailing because of its streamlined longitudinal shape when upright and when heeled over.
However, displacement mono-hulled sailing craft as described above are not suitable to be mechanically propelled at high speeds. When mechanical propulsion means, for example an outboard motor or a screw, provide high levels of forward thrust to the after end of the hull, the bow is forced out of the water and the aft sinks lower into the water. This slows the craft because its forward facing profile is increased, which results in a greater resistance against the water. The more power which is provided to the after end of the hull, the greater the bow lift and the water resistance. As a result the maximum speed which can be reached is fixed, regardless of the size of the engine. The object of the present invention is to overcome some of these problems and provide a watercraft with a displacement hull which may be used for sailing and be mechanically propelled at high speeds.
2. Description of the Related Art
A previous attempt to provide a watercraft which may be used for sailing and be mechanically propelled at high speeds is shown in shown in GB2150890 in the name of LANCER YACHT CORPORATION.
GB2150890 discloses a combination sailboat-powerboat hull in the form of a round-bottom, ballasted displacement hull, which is provided with generally horizontal foils which extend along the static water line on both sides of the hull, the forward ends of the foils being faired into the hillsides approximately amidships from where the foils extend rearwardly towards the quarters, and the foils extending out from the hullsides a distance less than the thickness of the boundary layer at sailing hull speed, the undersurface area of the foils being such as to enable the hull to plane when driven under auxiliary power.
It has been found that the watercraft disclosed in GB2150890 does not work as claimed. The “foils” described therein are planing surfaces which project from the hull and disrupt its streamlined shape. As a result the “foils” create drag which is detrimental to the performance of the craft when sailed and in particular when heeled over.
In order to minimise this drag, the “foils” are narrow in shape and do not extend through the boundary layer into the laminar zone. As a result the lifting force provided by the “foils” as they plane over the water when the craft is powered by a motor is very small and does not prevent the aft of the craft from sinking lower into the water.
Therefore, in an attempt to minimise the disruptive effect of the “foils” when sailing, they are made so small as to render the invention redundant.
The present invention is intended to provide a novel approach.